Apparatus for refining rare refractory metals



July 10, 1956 D. WROUGHTON ET AL 2,754,347

APPARATUS FOR REFINING RARE REFRACTORY METALS 2 Sheets-Sneet l FiledApril 28, 1944 I I .I

July 10, 1956 D. WROUGHTON ET AL APPARATUS FOR REFINING RARE REFRACTORYMETALS Filed April 28, 1944 2 Sheets-Sheet 2 aM/fam ATTORNEY DonaldWrougllton, Verona, and John W. Marden, East Orange, N. J., assignors,by mesne assignments, to the United States of America as represented bythe United States Atomic Energy Commission Applicaiion April 2s, 1944,serial No. 533,240

2 Claims. (ci. 13-33) This invention relates to apparatus for refining arare refractory metal such as uranium and more particularly to apparatusfor melting and casting such a metal in coalescent form.

in a copending application of William C. Lilliendahl et al., Serial No.478,270, filed March 6, 1943, now Letters Patent No. 2,690,421, issuedSeptember 28, 1954, a method is described whereby uranium may beprepared in the form of a compressed coherent powder. Briefly, themethod thereof includes the electrolysis of potassium uranous fluoride,KUFs, uranium tetrachloride, UC14, or uranium tetrafluoride, UF4, in afused salt bath of sodium and calcium chlorides in which uranium isdeposited on the cathode in the form of a powder, the separation of thepowder from soluble impurities by grinding and washing with water andacid, and finally the compression of the uranium powder into a slug orbutton while protecting it from oxidation. By heating said uraniumbutton to sintering temperature in a high vacuum as described in UnitedStates Letters Patent No. 1,814,719 to J. W. Marden et al., manyvaporizable impurities may be eliminated from the button, butnon-vaporizable impurities remain in the sintered mass. Such impuritiescannot be tolerated in certain uses of uranium. In a copendingapplication of George Meister, Serial No. 525,601 filed March 8, 1944,methods are described for rening and purifying uranium powder producedby electrolysis or produced by other reduction processes. Briey, themethods thereof include the melting of such uranium in a fused salt bathin air, vacuum or inert gases to remove oxides, salts and any otherimpurities to obtain uranium in a substantially pure coalescent form.The present invention relates to improvements in apparatus for refiningand purifying rare refractory metals in accordance with the methods setforth in said copending Meister application.

The present invention provides apparatus for melting and fusing a rarerefractory metal such as uranium to free it from vaporizable impurities,salts, and slags, to produce substantially pure metal in coalescent formwhich may be cast in any desired shape or form. The apparatus disclosedherein may be used in air without requiring the presence of inert gasesor vacuum conditions, and may be constructed from easily obtainablematerials, including carbon or graphite, at relatively low cost.

t is the general object of this invention to provide apparatus forrefining and purifying a rare refractory metal such as uranium, wherebythe impurities are separated from the metal while fusing the metal.

1t is an object of this invention to provide apparatus for fusing impureuranium powder to obtain uranium in coalescent form.

It is another object of this invention to provide ap-v paratus suitablefor purifying and fusing uranium or the like in a fused salt bath.

It is still another object of this invention to provide an apparatus forrefining impure uranium or the like at temperatures above the meltingpoint` thereof.

2,754,347 Patented July 10, 1956 Other objects and advantages of theinvention will be readily apparent to those skilled in the art from thefollowing description of preferred embodiments of apparatus illustratedin the accompanying drawings, in which:

Fig. 1 is an elevational view in section of a preferred form ofpurifying and fusing apparatus. Figs. 2, 3, 4 and 5 are elevationalviews in section of modified crucibles suitable for use in the apparatusof Fig. l. Fig. 6 is an elevational view in section of a modified formof purifying and casting apparatus. Fig. 7 is an elevational View insection taken on line 7--7 of Fig. 8 of a furnace for use with cruciblesof the types shown in Figs. 2, 3, 4 and 5. Fig. 8 is a plan view insection taken on line 8 8 of the apparatus shown in Fig. 7.

Referring to Fig. 1 of the drawings, a melting crucible is indicated bythe numeral 10. The crucible 10 is contained within a furnace having abase 11, a tubular member 12, an upper member 13, and a cover 14. Asupporting member 1S, cylindrical in shape, may be provided between thebase 11 and the bottom of the crucible 10 to support the crucible. Heatinsulating material 16 is also placed in the space between crucible 10and base 11. A high-frequency induction coil 17 having electrical leads17a and 17]) surrounds the cylindrical member 12 for heating thecontents of the crucible 10.

The materials used in both the crucible and furnace construction must becarefully selected because of the relatively high temperaturesencountered and because of the nature of the substances treated withinthe crucible. The crucible 10 may be made of carbon or graphite, thelatter being preferred. The base 11 and member 12 may be of Transite, orof similar heat resisting material. The cylindrical member 12 should beof material resistant to high temperatures, such as alundum or silica.The cover plate 14 should also be of refractory material, and thematerial 16 under the crucible should be heat insulating, such asasbestos, Silo-cel, or the like. The high frequency oscillator coil 17may be of any well known type, air or water cooled if desired, and maybe replaced by glow bars or resistance heating units, as will beapparent to those skilled in the art.

The mode of operation of the apparatus of Fig. 1 for refining uraniummay be as described in the methods disclosed in the above-mentionedcopending application of Meister, Serial No. 525,601. The crucible 10,which may be of any desired size, for example, 2% to 10 inches indiameter and 5 to 30 inches deep, is partially filled with saltssuitable for the melting bath. Various salts such as sodium chloride,NaCl, calcium chloride, CaClz, barium chloride, BaClz, sodium fiuoride,NaF, calcium uoride, CaFz, barium fluoride, BaF2, magnesium fluoride,MgFz, potassium acid fluoride, KHFz, alone or in cornbination, and alsothese salts together with small percentages of uranium, tetrafiuoride,UF4, may be used. Other salts such as phosphates, borates, hydroxides,and the like may also be satisfactory. The salts in the crucible areheated and fused by means of the coil 17, glow bars, resistance heatingelements, or the like. When the salt bath is fused and at a temperatureof the order of 1000 to 1100 C., electrolytically deposited uranim, orimpure uranium produced by other methods, is fed into the salt bathcontained in the crucible 10. The bath temperature may then be raised,by means of coil 17, to bring the temperature of the charge to about1200 C., at which point it is maintained for about ten minutes while thecharge is stirred with a carbon rod. During this time, the uranium inthe charge is fused and coalesces as substantially pure liquid in thebottom of crucible 10, as indicated by the numeral 18 in Fig. l. Some ofthe impurities present in the uranium charge are apparently converted tovolatilizable halides which are emitted from the bath. Other impuritiesappear to collect as a slag 19 above the molten uranium y18. The saltbath appar.- ently collects at the upper portion of the contents of theCrucible as a salt layer 20.

After the fusing and refining of the uranium charge has taken placesubstantially as described above, the pure coalescent uranium may berecovered by allowing the apparatus to Cool and the Crucible contents tosolidify. The salt and slag layers effectively prevent oxidation of theuranium being treated. After the Crucible contents have solidified, theCrucible may be broken apart and the uranium slug recovered from thebottom of the Crucible.V

In the event that crucibles having a bottom tap or a pour,- ing lip areused, as will be described hereinafter, the molten uranium in the bottomof the Crucible may be run into a suitable mold for casting in a desiredshape without solidifying in the Crucible itself.

Referring again to the accompanying drawings, modied forms of meltingCrucibles are illustrated in Figs. 2, 3, 4 and 5. The Crucible 2l ofFig. 2 is provided with a bottom tap or opening normally Closed by aplug 22 integral with or carried by a rod actuator 23. An inclinedinsert Z4 may be provided in the bottom of the Crucible 2l to Cause themelted metal to flow to the bottom tap when the plug 22 is raised by therod 23. The insert 24 should be secured in the bottom of the Crucible bytight lit or by a dowel or the like. The Crucible 2l, plug 22, rod 7,3,and insert 24 are preferably made from graphite, or from otherrefractory materialsrinert to the salt bath and rare refractory metalssuch as uranium at high temperatures. Vl/hen using the Crucible 2l, thefurnace of Fig. 1 may be modified, for example, as shown in Fig. 7described hereinafter, to receive a suitable mold located below the tapclosed by plug 22. Y

The Crucible 2:3, shown in Fig. 3, has a modified bottom surfaceprovided by a tapered portion 26. The tapered bottom portion 26 ofCrucible 25 provides a small volume space facilitating the fusing andCoalescing of the molten metal as the metal settles to the bottoni ofthe fused salt bath contained in the Crucible. Crucible 25 is preferablyformed of graphite.

ln the Fig. 4 embodiment, the Crucible 27 is similar to Crucible 10 ofFig. 1, and is provided with a cupped insert 28, also of graphite,suitably secured in the bottom of the Crucible. The insert 2b has asmall area recess 29 with tapered edges to provide a pool of crosssectional area less than the cross sectional area of the interior of theCrucible 27 to assist in the collecting and coalescing of the moltenmetal.

The Crucible 3o, shown in Fig. 5, is provided with a rotatable closureplug 3l positioned in the bottom tap or opening to Control the tappingof molten metal through a Crucible passage 32. The inner bottom portionof the Crucible 35; may 'oe tapered as shown, similar to the Fig. 3construction. Means such as the bar 33 may be provided for turning theplug 3l from a closed position to the open position illustrated. Asuitable mold may be positioned below the passage 32 for casting themoltenV uranium, as mentioned in Connection with the description of theFig. 2 construction.

The modified apparatus shown in Fig. 6 includes a Crucible 35 positionedin a tubular member of refractory material. The member 36 is providedwith a base plate 3'7 and an upper support plate 38, the latter beingconnected to a fixed pivot 39 whereby the furnace and Crucible may betilted. insulating material i9 is positioned below the Crucible 35, andheating means, such as the oscillator coil 4l surrounds the member 36.YA refractory cover plate 42 may be used to close the upper end ofmember 35. A graphite pouring tube 43 is secured to the upper end ofCrucible 35' and extends outwardly therefrom at approximately rightangles to the axis of the Crucible. A lip i4 may be provided on theupper end of Crucible 35 to avoid spilling the fused "salt bath from theCrucible when the apparatus is tilted to. pourV molten 'niiet-alfrom"'tlf'bath.` HAu refractory is provided to receive the molten metalfrom the pouring tube 43, and may be supported in a refractory cup 46positioned on a support 47. A rigid support 4S is provided to engage thebase plate 37 for supporting the fur nace in the upright positionillustrated.

The mode of operation of the apparatus of Fig. 6 is generally similar tothe operation of the apparatus of Fig. l, in that the Crucible 35 ispartially filled with salts suitable for the melting bath. The salts inCrucible 35 are heated and fused by means of the coil lil, glow bars,resistance units, or the like. When the fused salt bath temperature isof the order of 1100" C., the impure rare refractory metal such asuranium is fed into the bath and stirred if necessary while thetemperature is increased and maintained at about 1200 C. Thesubstantially puren metal collected in the bottomn of nthe Crucible 35is recovered by tilting the furnace about pivot 3Q until the CrucibleContents run out through the pouring tube i3 into the mold 45. Since themold 45 is smaller in size than the Crucible 35, the fused salt bath andslag may overrun the top of the mold 45 and be Collected intheVsurrounding cup 46 for further use. After the pouring and Castingoperation, the furnace is tilted back to the upright positionillustrated, against the support stop 48, and is ready for anotherCharge of salt and metal.

The apparatus shown in Figs. 7 and 8 provides a furnace heated by glowbars 5t) in place of high frequency oscillator coils. A graphiteCrucible 5l is positioned within the tubular member 52 of refractorymaterial. Insulating material 53 may be provided within the furnacecasing 54 and below the Crucible 51. Where the Crucible 51 is similar tothat described in connection with Figs. 2 and 5, a mold 5S.supported bya member 56 is postioned below the Crucible tap. A graphite tube 57 issecured to the upper end of the Crucible 51 and extends outwardly beyondthe furnace Casing. The tubular member 52 may be provided with aprojecting sleeve 58 of similar material surrounding the tube 57. Thegraphite tube 57 serves to carry olf excess fused salts from theCrucible 51 in the event that the addition of metal to the fused saltbath raises'the bathlevel so high as to tend to overflow the Crucible.The glow bars'Stl may be Connected to a suitlable source of electriccurrent as is well known in the .heating art.

The mode of operation of the apparatus of Figs. 7 and 18 is similar tothe operation of the apparatus of Fig. l.

The excess of fused saltsthat may be present, when impure uranium isadded to the Crucible 51, overflows through the tube 57 and may beCollected for further use. After the metal has been refined in a fusedsalt bath contained in Crucible 51, the molten metal may be drawn offthrough the bottom tap of Crucible 51 into a mold 55. The Crucibles ofFigs. l, 2, 3, 4 and 5 may be substituted for the Crucible 51 in theglow bar heated furnace of Fig. 7 by slight adaptations that will bereadily apparent.

The substantially pure coalescent uranium resulting from the refining ofimpure uranium in the above-described apparatus may give a recovery of86% of the theoretical uranium content of the uranium salts charged intothe electrolysis bath of the process of the previously mentionedCopending William C. Lilliendahl et al. application. The yieldV is foundto be equal or better than that attained by subjecting electrolyticallydeposited uranium powder to the usual'washing, grinding and sinteringprocedure. The apparatus herein disclosed offers less opportunity forContamination of the uranium than is present in the washing and grindingprocedure. Electrode deposits of uranium powder may be quickly andefficiently refined and molded to produce a coalescent substantiallypure uranium which is suitable for many Commercial uses without furtherYrefining. The Crucible constructions shown and described have been foundto be economical A and to facilitate the continuous operation o f therefining furnace. The Crpcibles may A be readily withdrawn from thefurnace and another Crucible and charge inserted for continued refiningoperations. The novel Crucible shapes disclosed aid in the collection ofCoalescent uranium metal in the bottom of the Crucible under aprotecting blanket of slag and fused salts. The use of a vacuum or acirculated inert gas around the furnaces shown is not necessary sincethe fused salt bath protects the molten uranium from contact with air orother contaminating substances. However, the evolved volatile impuritiesgiven oif from the refining crucibles may be withdrawn by a vacuum ormay be swept away by an inert gas if desired. Recovery of the denseCoalescent body of uranium metal may be made by breaking open the Coolcrucible or by casting the uranium in a suitable mold, as describedhereinbefore. Although the furnace has been shown heated by either highfrequency induction or by glow bars, various other methods of heatingwill be readily apparent. Among these would be heating by passing aheavy alternating current between the Crucible and a central carbon rodinserted into the fused salt bath. Even with the tapping or castingoperation taking place in air, coalescent metal bodies of high purityand density are attained. The slag layer removed from the refiningCrucible may be returned to the electrolysis furnace for still furthereconomy.

Although only preferred apparatus and embodiments thereof have beendescribed, it will be understood that numerous variations andmodifications may be made without departing from the spirit and scope ofour invention as defined inthe appended claims.

We claim:

1. In apparatus for refining uranium or the like in a fused salt bath, agraphite Crucible and a graphite insert in the bottom of said Crucible,said insert having a sloping upper surface providing a pool of crosssectional area less than the cross sectional area of said Crucible forthe collection of Coalescent uranium or the like under a fused salt bathcontained in said Crucible.

2. Apparatus for refining uranium that includes an insulating base, atubular member of refractory material supported on said base, aremovable Cover supported on said tubular member and defining therewitha furnace chamber, a refractory Crucible removably positioned withinsaid furnace chamber, said Crucible having a tap at the bottom thereofand an insert having an inclined upper surface to provide a pooldraining toward said tap, means insertable in said Crucible for openingand closing said tap, a passageway extending through the furnace chamberand associated with the tap whereby material may be removed from theCrucible, heat insulating means intermediate t'he Crucible and basemember, and means surrounding the tubular member for electricallyheating said Crucible.

References Cited in the file of this patent UNITED STATES PATENTS243,788 Pedder July 5, 1881 1,112,993 Dunton Oct. 6, 1914 1,372,676 DeBats Mar. 29, 1921 1,378,189 Northrup May 17, 1921 1,423,501 McClainJuly 18, 1922 1,466,739 Nakamura Sept. 4, 1923 2,027,065 Sadtler Jan. 7,1936 FOREIGN PATENTS 361,607 Germany Mar. 7, 1922 524,198 Great BritainJuly 31, 1940

1. IN APPARATUS FOR REFINING URANIUM OF THE LIKE IN A FUSED SALT BATH, AGRAPHINE CRUCIBLE AND A GRAPHITE INSERT IN THE BOTTOM OF SAID CRUCIBLE,SAID INSERT HAVING A SLOPING UPPER SURFACE PROVIDING A POOL OF CROSSSECTIONAL AREA LESS THAN THE CROSS SECTIONAL AREA FO SAID CRUCIBLE FORTHE COLLECTION OF COALESCENT URANIUM OR THE LIKE UNDER A FUSED SALT BATHCONTAINED IN SAID CRUCIBLE.